Processing of radioactive liquids



y 16, 1 s. A. PoDBEREsKY ETAL 3,320,175

PROCESSING OF RADIOACTIVE LIQUIDS Filed July 5, 1961 2 Sheets-Sheet 1 sR O T N E V N BERNARD A. PODBERESKY HARRISON T. LOESER THEIR ATTORNEYSMay 16, 1967 B. A. PODBERESKY ETAL 3,329,175

PROCESSING OF RADIOACTIVE LIQUIDS 2 Sheets-Sheet 2 Filed July 5, 1961wiozumwum 02m JOEFZOU U2 awwuoma INVENTORS BERNARD APODBERESKY HARRISONT. LOESER BY @AMW, JQW M THEIR ATTORNEYS United States Patent 3,320,175PROCESSHNG OF RADIOACTIVE LIQUIDS Bernard A. Porlbereslry, Norwich, andHarrison T. Loeser,

Waterford, Conn, assignors to General Dynamics Corporation, New York,N.Y., a corporation of Delaware Filed July 5, 1961, Ser. No. 122,012 3Claims. (Cl. 252-301.1)

(a) evaporation (b) crystalliaztion (c) demineralization (d) fixation(e) 'centrifugation These methods suffer from the disadvantage that thehighly radioactive residues remaining after processing are in a formwhich is difficult for handling and storage. Furthermore, the methodsare costly since they utilize relatively expensive material andequipment.

Demineralization with ion exchange resins is somewhat limited in itsapplication to radioactive liquid wastes since the regeneration of theexhausted resin produces highly radioactive liquids which themselvesmust be processed or stored in shielded tanks. In addition, replacementof the resin involves elaborate and expensive packaging of the exhaustedresin for burial. Still another advantage in using ion exchange resinfor processing radioactive liquid wastes is the direct effects ofradiation on the resin resulting in a decrease in the exchange capacityand degradation of the physical and chemical characteristics of theresin.

Thus, a demand exists in the nuclear industry for a more efficient andeconomical method of removing radioactive ions from liquid wastes.

It is an object of this invention to provide an economical and efiicientmethod for decontaminating batch quantities or flowing streams ofradioactive liquid wastes.

It is another object to provide a novel means for placing certainradioactive isotopes in a form for use as radiation sources.

A further object of this invention is to provide means for removingradioactive ions from a liquid and placing them in a convenient form forhandling and storage.

Still another object is to provide a means for augmentingdemineralization of radioactive liquid Wastes and increasing theoperating life of ion exchange demineralizers.

These and other objects and advantages are realized by the applicationof an electric field to liquid wastes containing radioactive ions toremove the ions from the solution.

This invention may be better understood from the following detaileddescription taken in conjunction with the accompanying drawings inwhich:

FIG. 1 is a perspective view of a unit for processing a batch ofradioactive liquid wastes;

FIG. 2 is a diagrammatic sketch of asystem for processing a continuousflow of radioactive liquid waste materials;

FIG. 3 represents an end view of an electrode found suitable for use ineither a batch or flow-type processing unit of this invention;

FIG. 4 is a side view of the housing designed for use with a flow-typeprocessing unit of this invention; and

3,3Z,i?5 Patented May 16, 1967 FIG. 5 is a view of a section taken on aplane represented by the line 5-5 of FIG. 4 looking in the direction ofthe arrows.

An illustrative embodiment of the present invention includes a containerwith electrodes to provide a potential gradient therebetween. When asolution containing radioactive ions is brought into contact with theelectrodes, the radioactive metallic ions present are deposited on theelectrodes and thus etficiently and quickly removed from the solution.

One embodiment of this invention involves the use of sacrificial anodeswhich go into solution during the period in which a potential is appliedacross the electrodes. This feature provides additional ions in thesolution to replace the radioactive metallic ions being removed andenables the process to proceed at a more efiicient rate.

A further advantage in the use of sacrificial anodes lies in the removalof non-metallic radioactive isotopes from liquid wastes by combinationof the non-metallic radioactive ions with the ions of the sacrificialanodes to form an insoluble precipitate. An example of this particularembodiment is the removal of radioactive sulphur in the form of a coppersulfate precipitate when the solubility product of the latter isexceeded.

The use of properly designed sacrificial anodes will not reduce theoperating life of the processing unit. By preliminary testing andevaluation, anodes can be properly sized in thickness to operateefiiciently in a processing unit for lengthy periods before beingexhausted.

In the processing of liquids containing radioactive cobalt, there is atendency toward the formation of insoluble cobaltic hydroxide by virtueof the oxidation of cobaltous ion to cobaltic ion, and subsequentcombination with hydroxyl ion present in the liquid. This formation of aprecipitate supplements the removal of cobalt by deposition on thecathode and serves to increase the etficiency of the method. Otherradioactive ions which form insoluble precipitates in a manner similarto that of cobalt may likewise be removed from waste liquids.

The present invention may be made to operate even more efiiciently inmany instances by the addition of certain chemicals to the liquid being:processed. The use of such additives to control conditions such as pHand ion concentration forms an important subsidiary feature of theinvention. Thus, the addition of a chemical which suppliesnon-radioactive ions of the radioactive isotope being removed willincrease the rate of deposition and permit more rapid removal of agreater percentage of the radioactive ions A very important advantage oftheinvention is its adaptation to a continuous or batch operation. Aflowing stream or a single batch of radioactive waste can be quickly andefficiently decontaminated by the present method. FIG. 1 shows apparatussuitable for processing a batch of waste material, which includes acontainer 10, adapted to hold a liquid 11 to be processed. The anodes 12are made of inert material such as carbon and cathodes 13 are in theform of conductive metal plates. The anodes 12 and cathodes 13 aresuspended from mental bars 14 attached to the rim 15 of the container10. In the particular embodiment depicted in FIG. 1, two cathodes 13 arepositioned directly opposite each anode 12.

In FIG. 2 there is depicted a system which has been efiiciently used inprocessing a continuous flow of material. The initial reservoir 16contains the liquid waste to be processed. The pump 17 pumps the liquidthrough processing units 18 and 19 connected in series for greaterefficiency and then ultimately to the final reservoir 20. The filtersshown at 21 and 22 act to remove precipitates formed during theprocessing. In this embodiment the control unit 23 for the operation isremoved from the immediate vicinity of the actual processing equipmentto eliminate radiation danger to operating personnel. If desired, theliquid may be recycled by returning it to the initial reservoir from thefinal reservoir and the process repeated. The sampling line 24 permitsremoval of portions of the processed liquid for determination of theradioactive isotope content.

Processing units may be connected in series for greater operatingefliciency. Furthermore, the control unit for operating the continuoussystem does not require radiation shielding to protect operatingpersonnel, since the control unit can be separated from the processingunit or units, as shown in FIG. 2. The most eificient use of the methodof the invention requires testing a sample of the liquid waste initiallyto determine optimum operating conditions and selection of properelectrode material.

The present invention not only provides an economical and efiicientmeans for decontaminating radioactive liquid wastes, but the compactform of the deposited radioactive material facilitates handling andstorage of the material. Since the radioactive isotopes are concentratedwithin a relatively small area, the protective shielding normallyrequired can be substantially reduced. Furthermore, the processingequipment is not subjected to degradation by the effects of radiation tothe extent noted in other processing operations such as where ionexchange resins have been utilized.

Another important advantage of the invention is the fact that undercertain easily-determined operating conditions, the radioactive materialis in the form of finegrained adherent deposits which can be utilized asa source of radiation. Thus, the radioactive isotopes are recovered fromliquid wastes and made to serve a useful purpose. Other operatingconditions will result in the production of non-adherent deposits ofradioactive materil which are swept away from the electrode and trappedin a filter thus extending the operating life of the unit.

It should be realized that instead of replacing a demineralized with theprocessing unit of this invention, the operating life of the ionexchange resin can be extended by positioning a processing unit of thisinvention in front of the resin in the purification loop. In thismanner, the unit will supplement the resin by electro-deposition of ionswhich ordinarily occupy ion exchange resin sites in the demineralizer.

The design of the elect-rode is important if optimum operatingconditions are to be attained. FIG. 3 shows a wrap-around type electrodeconsisting of alternate layers of fiberglass insulation 25 and brasssheeting 26 rolled into a cylinder 27 to fit the particular housing ofthe processing unit. This design offers a large electrode surface areawith relatively close spacing.

FIG. 4 shows the construction of a container designed to house either awrap-around or cell-type electrode in a continuous operation. Thecontainer 28 is preferably constructed from a sturdy material such ascast iron. The electrical connections are made with the aid of aninsulated electrical penetration fitting 29. The waste material entersthe housing through the inflow conduit 30 and is removed by way of theoutflow conduit 31 after coming into contact with the electrodescontained within housing 28.

A cell-type electrode in cross-section is shown in FIG. 5. The electrode32 allows close electrode spacing and presents a large electrode areaper unit volume of liquid passing through the cell. It is constructed ofbrass plates 33 about 0.032 inch thick, with plastic strips 34 aboutinch thick used as insulators. The electrical connections are such thateach alternate electrode is of the same electrical polarity.

If desired, the electrode may be placed within a suitable container (notshown) which is then inserted into the housing structure depicted inFIG. 5. Of course, the inner container would be perforated to enable theradioactive eiiluent to contact the electrode.

The following examples further illustrate the invention. In theseexamples, the electrodes were chemically cleaned prior to the operation.Cleanliness of the electrodes is an important factor in obtaining goodadherent deposits.

Example 1 In this example, a solution containing metallic ions wastested in order to determine the feasibility of quickly and economicallyremoving radioactive ions from solution. Initial tests were run usingreactor grade water containing very small concentrations of radioctivecobalt. The concentration of cobalt was too dilute for accuratequantitative determination. By counting the gamma radioaction, it wasdetermined that approximately of the Co in solution was removed in 15minutes of operation. For convenience, the remaining tests wereconducted with non-radioactive ions.

Example 2 The cathodes of the processing unit were various metal platessuch as copper while the anodes were inert carbon plates. The electrodeswere suspended from copper bars in a tank as shown in FIG. 1. Eachcarbon anode was positioned directly opposite two metal cathodes withthe distance between the anodes and cathodes being approximately threeinches.

A batch of solution was prepared containing ions of cobalt and iron andwas processed utilizing the batch unit. Both cobalt and iron weredeposited from the solution on the cathodes when a current of 400milliamperes was applied. This mixed ion solution contained thefollowing components:

CoSO -7H O 252 NaCl 7 H 30 28 Feclg' KCl Example 3 The followingsolution was processed using a batch type unit as shown in FIG. 1:

Cobaltous sulfate-7161 0 g./l 2 Sodium chloride mg./l Boric acid mg./l200 The boric acid additive acted as a buffering agent. A receptacle wasfilled with this cobalt solution and a wrap around type electrodeconstructed as shown in FIG. 3 was introduced into the container. Acurrent of about 300 milliamperes was supplied to the electrodes (1.29rna./cm. After about 30 seconds of operation, the characteristic pinkcolor of the cobalt solution disappeared indicating that a largepercentage of the cobalt ions in the solution had been removed. Afterthe electrode was withdrawn, a brownish-colored precipitate wasdiscovered suspended in the treated solution. This suspendedprecipitate, identified as cobaltic hydroxide, was removed from thetreated solution by filtration. The filtered solution was analyzed todetermine the amount of cobalt remaining in the solution afterprocessing. The result of the analysis is as follows:

00 Content Before Processing (p.p.m.)

00 Content After Processing (p.p.m.)

Percent Removed 1 This series of experiments in the second line utilizeda double fiberglass screening rather than a single layer as insulation.

The extraordinary efficiency of the method of the present invention isclearly illustrated by this example. A thirty second operation resultedin almost complete removal of the cobalt isotope.

Example 4 In this example, a flow model processing unit as de scribed inFIG. 4 was used to process a continuous stream of material. Afive-micron filter was installed in the processing loop downstream fromthe unit to remove the hydroxide precipitate. Other components in theprocessing loop included a 4.5 gallon/minute pump, a flowrneter, atwenty-micron pre-filter, the processing unit itself and the necessarycontrol equipment. Initial tests were conducted using a wrap-around typeelectrode installed in the processing unit housing. With both thepre-filter and post-filter in the test loop, the maximum flow rateobtained was one gallon per minute. The unit performed well for severalminutes using a current of 800 milliamperes (0.14 ma./cm. and a currentof 500 milliamperes (0.09 ma./cm. After several minutes operation,however, the unit removal effectiveness decreased. It was noted that thefiberglass screening used as the insulation on the electrode hadretained a considerable amount of fluid. The water-filled insulationapparently acted as a physical barrier tending to prevent the migrationof the ions to the electrodes and decreasing the electrodepositionprocess. After the fiberglass insulation had been allowed to dry, theelectrode again operated effectively.

Because of the high pressure drops in the system, the five-micron postfilter was removed from the loop and replaced with a twenty-micronfilter. This larger post filter eliminated the need for a pre-filter.With the five micron filter removed, a two gallons per minute flow ratewas realized. A cell-type electrode was then substituted for thewrap-around electrode. This electrode was positioned in the housing ofthe unit and the necessary electrical connection made by use of thefitting as shown in FIGURES 4 and 5. The pump was ultimately bypassed todecrease the flow rate even further and provide a gravity feed system.After several minutes of efficient processing under an applied currentof 800 milliamperes (0.52 ma./ cm. a greenish foam developed whichproved to be copper sulfate and which was removed by providing a hole inthe housing cap. This outlet became the liquid and foam outlet to thefilter and the former outlet tube was used as a sampling line. With thesystem reassembled and the unit operated at 800 milliamperes, aconsiderable amount of foam and precipitate was observed in the outletline to the post filter.

The following cobalt solution was processed using this flow model unit:

CoSO -7H O g./l 2 NaCl mg./l 100 H3303 mg./l

The results are as follows: Co content original solution (p.p.rn.) 315 6First pass (p.p.m.): Percent removed 71.5 Final pass (p.p.m.):

It can readily be seen that the present invention is extremely versatilein its application to the processing of wastes containing radioactiveions in solution.

While particular embodiments of the present invention are shown anddescribed for purposes of illustration, it is apparent that changes andmodification may be made Without departing from this invention in itsbroader aspects. Therefore, the invention described herein is not to beconstrued as limited to the specific embodiments described, but isintended to encompass all modifications thereof coming within the scopeof the following claims.

We claim:

1. A method for processing radioactive liquid wastes which comprisescontacting a liquid containing radioactive non-metallic ions withelectrodes including at least one anode and one cathode, the anode beingfabricated from a metal which is reduced and goes into solution therebycombining with the non-metallic ions to form an insoluble precipitate.

2. A method for processing radioactive liquid wastes containingradioactive cobalt which comprises contacting a liquid Waste materialcontaining a radioactive isotope of cobalt with electrodes andsimultaneously depositing the cobalt on the cathode and precipitatingcobalt in the form of cobaltic hydroxide.

3. A method for processing radioactive liquid wastes containingradioactive sulphur which comprises contacting a liquid waste materialcontaining a radioactive isotope of sulphur with electrodes including atleast one anode and one cathode, the anode containing copper, therebyprecipitating sulphur in the form of copper sulfate.

References Cited by the Examiner UNITED STATES PATENTS 2,116,138 5/1938Boss 204 275 2,299,964 10/1942 Grouch 204-149 2,399,389 4/1946 Negus204-275 2,737,298 3/1956 Handel 204-449 2,854,315 9/1958 Alteretal.

OTHER REFERENCES Messing et al.: ORNL-2532, An Electrolytic Procedurefor the Removal of Ruthenium and Nitrate from Alkaline Waste Solutions,Oak Ridge National Laboratory, 1958, pp. I7 and 20-23.

L. DEWAYNERUTLEDGE, Primary Examiner.

JOSEPH REBOLD, LEON D. ROSDOL, BENJAMIN R. PADGETT, Examiners.

" T. TUNG, L. A. SEBASTIAN, Assistant Examiners.

1. A METHOD FOR PROCESSING RADIOACTIVE LIQUID WASTES WHICH COMPRISESCONTACTING A LIQUID CONTAINING RADIOACTIVE NON-METALLIC IONS WITHELECTRODES INCLUDING AT LEAST ONE ANODE AND ONE CATHODE, THE ANODE BEINGFABRICATED FROM A METAL WHICH IS REDUCED AND GOES INTO SOLUTION THEREBYCOMBINING WITH THE NON-METALLIC IONS TO FORM AND INSOLUBLE PRECIPITATE.